1. Field of the Invention
The present invention is a system and method for measuring regression of a material by determining the length of optical waveguides mated to the material in a high erosion environment. More specifically, the present invention may be used to determine the burn rate, or regression rate, of a solid fuel rocket motor, braking system, or any other regressable material in a volatile environment by dividing the change in length of the waveguides by the change in time.
2. Description of the Related Art
A solid rocket or a solid fuel rocket is a rocket with a motor that uses solid propellants—fuel and oxidizer. Solid rockets are simple, reliable, and well-known in the prior art, but because of the highly volatile and high temperature environment of combusting solid fuel in the rocket motor, precise measurement of the rate of consumption of the fuel, termed “regression” or “regression rate,” is difficult. More precise information than is currently available by methods and devices used in the art would be of benefit to the engineers and scientists who design solid fuel rocket motors.
A simple solid rocket motor consists of a casing, nozzle, grain (propellant charge), and igniter. The grain behaves like a solid mass, burning in a predictable fashion and producing exhaust gases, and is usually molded from a thermoset elastomer, fuel, oxidizer and catalyst. For example, hydroxyl-terminated polybutadiene (HTPB) and polybutadience acrylonitrile (PBAN) are typical elastomers that double as fuel. Ammonium perchlorate is the most common oxidizer. The nozzle dimensions are calculated to maintain a designed chamber pressure, while producing thrust from the exhaust gases.
Not surprisingly, rocket engineers have long had difficulty measuring the burn rate, also called the regression rate, of the materials due to the volatile nature of a combusting solid rocket motor, which makes measurements of its characteristics during combustion very difficult. Not only must any measuring system be capable of operating in and withstanding the high temperature and violent environment, but such a system must also not affect the operating conditions within the rocket. In other words, such a system must be designed around the inherent dangers of operating in such a combustible environment. For example, electromagnetic interference (EMI), which can cause disruption of electronic components, is generally not desirable within such a sensitive environment.
More precise measurement of the regression rate within the rocket motor would serve at least two useful purposes. First, such a measurement would increase the ability of rocket engineers to design solid rocket motors. A large part of the current design process is trial and error: The engineers will design a solid rocket motor but have no way to accurately test how the fuel grain burns without launching the rocket. Not only is this very expensive, but it is also very time consuming. The present invention, by providing engineers with more accurate measurement of the firing characteristics of the motor, reduces the need for trial and error during the design process, in part by allowing more accurate measurement of burn rate characteristics during test flights.
Second, such precise measurements would provide data to engineers during rocket operation that may indicate a potential problem with a rocket motor, or even worse, a catastrophic event. By using one or more of the measurement systems described herein, burn characteristics can be extrapolated and analyzed to determine whether motor operation is faulty. For example, one such a potentially catastrophic event is termed “asymmetrical burn,” wherein the solid rocket motor burns at different and unintended rates throughout, which could cause the rocket, inter alia, to move off course or have other adverse effects.
Accordingly, the present invention provides a system for, inter alia, measuring the regression rate in a solid rocket motor as it combusts, as well as measuring erosion of materials in other volatile environments.